I used to love performing this trick. Theres also a great version of this trick in plastic with different color gems that I used to use as a lead in to Hot Rod.

The Mint Looks like this. you start off w/ a cube of silver. You roll the cube between your hands and it smooths out and changes into a ball of silver. You then smash your hand against the al and it flattens out into a disc. You then squeeze it and it changes into a coin.